Ferritins, the main intracellular iron storage proteins, have been studied for over 60 years, mainly focusing on the mammalian ones. This allowed the elucidation of the structure of these proteins and the mechanisms regulating their iron incorporation and mineralization. However, ferritin is present in most, although not all, eukaryotic cells, comprising monocellular and multicellular invertebrates and vertebrates. The aim of this review is to provide an update on the general properties of ferritins that are common to various eukaryotic phyla (except plants), and to give an overview on the structure, function and regulation of ferritins. An update on the animal models that were used to characterize H, L and mitochondrial ferritins is also provided. The data show that ferritin structure is highly conserved among different phyla. It exerts an important cytoprotective function against oxidative damage and plays a role in innate immunity, where it also contributes to prevent parenchymal tissue from the cytotoxicity of pro-inflammatory agonists released by the activation of the immune response activation. Less clear are the properties of the secretory ferritins expressed by insects and molluscs, which may be important for understanding the role played by serum ferritin in mammals.